Method of eliminating aluminate and silicate inclusions



Patented Oct. 17, 1944 METHOD OF ELIMIINATING ALUMINATE I AND SILICATE INCLUSIONS Harold E. Phelps, Detroit, Mich, assignor to The Cerium Corporation, tion of Illinois Chicago, 111., a corpora- No Drawing. Application November 27, 1942,

Serial No. 467,152

Claims.

The invention relates generally to a method of refining steel and has more particular reference to an improved refining method which will produce a'high quality steel that will be clean as judged by microscopic, macroscopic or magnafiux methods.

In the production of high quality steel the elimination of non-metallic inclusions is of the utmost importance. In fact, cleanliness in steel is in direct proportion to the absence of these inclusions. It is now universally recognized that many previous unexplained failures of steel have been due to these occluded oxidized particles, which may be considered as primarily the oxides of aluminum and silicon. The proportion of such particles in the ingot depends largely on the precautions taken during final stages in the steel making process, the opportunity allowed for the inclusions to separate out before and during teeming, and the care with which thefinal' deoxidizers such as aluminum, silicon .and zirconium are added to quiet the steel.

Since it has been known that the formation of inclusions in molten steel is largely due to the content of 'the steel by usual steel making processes before the final deoxidizers are. added. Thus, certain-methods maintain a reducing or deoxidizing slag for keeping the oxygen'content' I of the steel to a minimum. Other methods cantemplate the use of pure raw materials by which the bath' is oxidized to a minimum degree previous to final treatments. Final deoxidizers in a combined form, as alloys of iron, are also used. Thus ferro-silicon and ferro-aluminum and similar metals have been used in the final treatment for deoxidizing the steel.

The present invention aims to provide animproved refining method for producing a high quality, sound and clean steel by eliminating to a substantial degree the harmful non-metallic inclusions in the steel, and which'will have application to present day steel making processes.

A further object is to .provide an improved refining method whichwill increase the'y ield of I sound clean steel in the ingot by approximately 50 percentage of cerium is a factor in the invention since it results in the production of a minimum' ten per cent. I a I The invention proposes to reduce the inclusions while the steel is in a molten state by chemical combination with one of the rare earthmetals, preferably cerium. The addition of cerium to killed steels in amounts of from -.01%

'to 1.00% almost entirely eliminates the oxides, such as those of aluminum and silicon, namely, A120: and SiOz, through chemical combination of the cerium with the oxygen of the inclusion. This reduction of the aluminum and silicon oxides, liberates the metals so that they are free to alloy with'the steel. The same chemical combination takes place with respect to othe Ox des that'may be present in the molten steel. Their reduction freesthe metal which is kept in solution in the steel.

Cerium oxides and sulphides are formed when cerium is used asthe rare earth metal but the reaction products of this metalare not objectionable since they do not agglomerate and are small and well distributed in the steel, whereas, .the inclusions such as theoxides of aluminum, silicon and the other deoxidizers do agglomerate to-form stringers following the rolling operation and are tough, brittle particles, considerably harder than the steel itself In this way subsequent machining operations on the steel are substantially improved in addition to the fundamental improvement as a result of great cleanliness.

By reducing these hard, brittle oxides a double advantage is secured since in the first place-the metal, whether it be aluminum, silicon or manganese, is liberated for alloying with the steel, which is desirable, and secondly, even though other oxides are formed, they are small, well dis- *tributed and therefore not detrimental.

In accordance with the invention the addition of cerium tothe molten steel takes place after the introduction oi the final deoxidizers for deoxidizing the metal and thus the refractory non-metallic inclusions comprising the reaction products of the final deoxidizers are preseat for chemical combination with the cerium. The cerium may be added to the ladle as the 40 heat is tapped, although it is also within the invention to add the cerium to the molten steel as it is poured into the ingot molds.

cerous fluoride having the chemical formula CeFs. This compound of cerium has a high melting point and the cerium is therefore liberated at the proper time for performing the functions desired.

The preferred amounts of cerium for various carbon steels is given in the table below, The low of cerium inclusions. Only enough cerium is 7 added for combining chemically with the oxygen of the non-metallic inclusions formed by the addition of the final deoxidizers to the molten steel.

Also the cerium can be added in uni/ form but-I prefer to use:

Steels up to .20% C .03% to .06% Ce Steels from .20% C to .60% C .02% to .04% Ce Steels over .60% C .01% to .03% Ce For controlling grain size it has been common practice to add predetermined quantities of aluminum to the steel. Some of this metallic alumi: num is oxidized, forming alumina inclusions, with the result that its function as a grain-size controlling element is lost in addition to the production of the undesirable alumina inclusions. The addition of cerium according to theinvention has a stabilizing action in fine grained steels through the ability of the cerium to reduce the A120: inclusions. The aluminum is thereby kept in solution in the steel.

Also the addition of cerium in amounts and in a manner herein described is especially beneficial in making high aluminum steels wherein the aluminumconstitutes an alloying constituent and may be present in quantities ranging from 1% to 1.5%. Such steels are known as nitriding steels, and in the past considerable trouble has been encountered in maintaining uniform aluminum content for all the ingots poured from any one particular heat. In other words, the aluminum content has generally been progressively lower in successive ingots. By the addition of cerium, the tailing off of aluminum in successive ingots is prevented and a uniform content of aluminum can be maintained for all the ingots poured from a heat.

The advantages claimed for the present invention have been proved in actual practice. Electric steel has been produced substantially free of harmful non-metallic inclusions. Also the yield per ingot for this clean steel has been increased by approximately ten percent.

What is claimed is:

1. The process of manufacturing a clean steel, which consists in preparing a molten bath of killed steel, adding cerium to the killed steel in amounts ranging from .01% to 1.00%, and then pouring said steel to produce ingots in the usual manner.

2. The process of manufacturing a clean steel, which consists in preparing a molten bath of killed steel, adding cerium to the killed steel in amounts ranging from .01% to 1.00%, said cerium being added in combined form as cerous fluoride having the chemical formula CeFz, and then pouring said steel to produce ingots in the usual manner.

3. The process of manufacturing a clean steel which consists in preparing a molten bath of killed steel, adding cerium to the killed steel to reduce the inclusions by chemical combination with the oxygen of the inclusion, said cerium being added in the following amounts for the various carbon steels:

Steels up to .20% C .03%'to .06% Ce Steels from .20% to .60% C .02% to .04% Ce Steels over .60% C .01% to .03% Ce 4. The improvement in the manufacture of steel, which consists in adding the usual deoxidizers to the molten metal and then adding cerium to the molten metal in the following approximate amounts for the various carbon steels: Steels up to .20% C .03% to .06% Ce Steels from .20% to .60% C .02% to .04% Ce Steels over .60% C .01% to .03% Ce said cerium being added in combined form as cerous fluoride having the chemical formula CeFa.

5. The process of manufacturing a clean steel free of harmful inclusions, which consists in adding the final deoxidizers such as aluminum and silicon to the-molten steel for deoxidizing the same whereby refractory non-metallic inclusions are formed in the molten steel as reaction products of the final deoxidizers, then adding cerium for chemically reacting with said non-metallic inclusions in the following approximate amounts for the various carbonsteels:

Steels up to .20% C .03% to..06% Ce Steels from .20% to .60% C .02% to .04% Ce Steels over .60% C .01% to .03% Ce said cerium having the effect of reducing the said non-metallic inclusions and of leaving in the steel a minimum of small, well distributed particles which are not detrimental nor harmful to the steel. v

' HAROLD E. PHELPS. 

